#include <iostream>
using namespace std;

int main() {
    std::string str = "Hello, world! Welcome to the C++ world.";
    
    // 查找最后一个逗号的位置
    size_t pos = str.find_last_of(',');
    if (pos != std::string::npos) {
        std::cout << "The last comma is at position: " << pos << std::endl;
    } else {
        std::cout << "No comma found." << std::endl;
    }
    
    return 0;
}